The present invention relates to the preparation of polymerisation catalysts, and in particular to the preparation of silicon containing transition metal catalyst components for use in the polymerisation of olefins.
In recent years there have been many advances in the production of polyolefin homopolymers and copolymers due to the introduction of metallocene catalysts. Metallocene catalysts offer the advantage of generally a higher activity than traditional Ziegler catalysts and are usually described as catalysts which are single site in nature.
There have been developed several different families of metallocene complexes. In earlier years catalysts based on bis (cyclopentadienyl) metal complexes were developed, examples of which may be found in EP 129368 or EP 206794. More recently complexes having a single or mono cyclopentadienyl ring have been developed. Such complexes have been referred to as ‘constrained geometry’ complexes and examples of these complexes may be found in EP 416815 or EP 420436. In both of these complexes the metal atom eg. zirconium is in the highest oxidation state.
Other complexes however have been developed in which the metal atom may be in a reduced oxidation state. Examples of both the bis (cyclopentadienyl) and mono (cyclopentadienyl) complexes have been described in WO 96/04290 and WO 95/00526 respectively.
The above metallocene complexes are utilised for polymerisation in the presence of a cocatalyst or activator. Typically activators are aluminoxanes, in particular methyl aluminoxane or compounds based on boron compounds. Examples of the latter are borates such as trialkyl-substituted ammonium tetraphenyl- or tetrafluorophenylborates. Catalyst systems incorporating such borate activators are described in EP 561479, EP 418044 and EP 551277.
The above metallocene complexes may be used for the polymerisation of olefins in solution, slurry or gas phase. When used in the slurry or gas phase the metallocene complex and/or the activator are suitably supported. Typical supports include inorganic oxides eg. silica or polymeric supports may alternatively be used.
Examples of the preparation of supported metallocene catalysts for the polymerisation of olefins may be found in WO 94/26793, WO 95/07939, WO 96/00245, WO 96/04318, WO 97/02297 and EP 642536.
Supported metallocene catalysts may be prepared by use of sol-gel techniques.
Silicate gels are typically prepared by hydrolyzing monomeric tetrafunctional alkoxide precursors utilizing a mineral acid or base as a catalyst. For example the hydrolysis and condensation of tetraethoxysilane in a sol-gel process catalysed by ammonia results in a sol-gel powder which may be used as an organometallic catalyst support.
In J. Applied Polymer Science Vol. 78, 2318-2326 (2000) there is described silica supports for metallocenes prepared by the gelation of a stable colloidal phase of silica using MgCl2 as initiator. Polymer Bulletin 46, 175-182 (2001) describes the synthesis of metallocene catalysts supported on silica type sol-gel carriers. The silica gels were prepared in a wet sol-gel procedure by hydrolysis and condensation of tetraethoxysilane in a mixture of water, ethyl alcohol and ammonia.
Polymer 42, 2001 pgs 4517-4525 describes the preparation of supported metallocenes by use of xerogels based on the hydroylsis and condensation reactions between tetraethoxysilane and bis(indenyl)diethoxysilane. In all the above preparations the resultant supported catalysts were employed in the polymerisation of ethylene.
Applied Catalysis 230, Pg. 287-302 (2001) describes indenyl-silica xerogels prepared by hydrolysis and polycondensation of bis(indenyl)diethoxysilanes and tetraethoxysilane.